Machine-switching telephone-exchange system



April 13 1926. 1,580,929

- R. L. STOKELY MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Original Filed April 20, 1921 I 4 Sheets-Sheet 1 fiyl.

4 Y .3 I Hp //7 ven for April 13 1926.

R. 1.. STOKELY MACHINE SWITCHING TELEPHONE'EXCHANGE SYSTEM Original Filed April 20} 1921 4 Sheets-Sheet 2 WNW April 13 1926.

v L. STOKELY MACHINE SWITCHING TELEPHQNE EXCHANGE SYSTEM o i i Filed April 20, 1921. 4 s ts-Sheet 3 s) v13 Wk Sh Rm Arty April 13,1926. 1,580,929

- R. L. STOKELY v MACHINE SWITCHING TELEPHONE EXCHANGE SYSTEM Original i e A ril 20. 1921 .4 Sheets-Sheet 4 iii Patented Apr. 13, 1926.

. UNlTED STATES. ATENT OFFICE.

. RAY L. STOKELY, or FLORAL PARK, LONG 1mm), YORK, Assrenon To WEST- nnn ELECTRIC COMPANY, moonronnrnn, or new YORK, N. Y., A oonronnrron OF NEW YORK.

MACHINE-SWITCHING 'rnnnri'ionn-nxonnnen SYSTEM.

Original application filed April 20, 1921, Serial No. 462,868. Divided and this application 'filed March To all whom it may concern: I I

Be it known that I, RAY L. STOKELY, a citizen of the United States of America, residing at Floral Park, Long Island, in the county of Nassau, State of New York, have invented certain new and useful Improvements in ldachineswitching Telephone-Ex change Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems employing machine switching and is a division of my application Serial No. l62,868 filed April 20, 1921, since issued as Patent 1,501,07 July 15, 1924."

The object or" this invention is to provide an improved circuit arrangement to take care of'toll calls to and from full automatic offices.

In the present system a toll operators dial is automatically connected to a desired trunk by inserting a. plug in the jack of said trunk and a supervisory lamp at the operators position is flashed to indicate a busy condition of either thecalled line or an intermediate trunk group. The supervisory lamp is also lighted upon the insertion of the operators plug in the jack of the trunk in case the distant automatic equipment is not in condition to receive dial impulses and remains so lighted until such distant equipment is ready for the impulses, or until the plug is removed from the ack at which time it is ex tinguished.

The principal feature of this invention, therefore, is the provision of means, at an operators position, to indicate when the distant automatic equipment is not in condition to receive dial impulses.

Referring to the drawings. Fig. 1 shows a toll cord circuit and part of a trunk outgo ing from the toll board to a full mechanical or automatic oflice; 2 shows an incoming selector at the full mechanical otlice; Fig. 3 shows a toll transmission selector repeater: Fig. 4: shows a combination toll and local connector.

The invention will be most readily understood from a description of the operation of the system.

The toll operator having been informed. for example, by the recording operator, of the number of the wanted line in the auto matic ofiice, tests for an idle trunk by toucli- Scrial No. 702,710.

ing the tip O'fher plug 100 to the sleeve of the jack 101 of the toll switching trunk and it she does not hear a click in her head set connected to the tip through a normal contact of relay 102 inserts the plug intofthe jack. The sleeve of. the plug applies potential to the sleeve of the jack to cause the seized trunk to test busy at the other toll operators positions. Relay 102 operates in series with relay F, disconnects the operatorshead set and connects the tip of the plug through to the bridged calling supervisory relay 103. Relay 104 is marginal and operates only when the plug is inserted into the jack of a toll line leading to a distant toll switchboard and under such circumstances cuts Oil the bridge containing relay 103 to prevent this bridge from shunting the alternating current applied by the operator at such distant toll switchboard to operate an alternating current relay (not shown) in the cord circuit. This isfin accordance with well-known practice. Relay F in attracting its inner right armature looks itself in series with relay C and in attracting its outer right armature operates relay G. Relay G locks itself in a circuit including the armature and normal contact of relay J, and operates relay H to open the bridge con taining relay J. Relay G at its right armatures interconnects the incoming and out going ends of the trunk and relay F at its outer and middle left armatures connects the impulse contact 106 of the toll operators dial 105 througlrrelays D and E to the impulse relay A of the incoming selector at the distant automatic ofi'ice. The dial is common to the trunks oi the position. He lays A and D operate in this circuit, but relay E is polarized, and. does not respond to this diretion of currentflow. Relay D to receive impulses from the dial. In case,

counters a busy trunk group, as will be later described. Relay B at its right armature closes a shunt around the right armature contact of relay A. Relay A operates the usual slow relay B which opens the circuit of the release magnet 24l0 and connects the vertical magnet 210 to the back contact of the impulse relay A in the well-known manner.

hen the operator rotates the dial for the first digit contact 108 closes, operating relay A which in attracting its inner armature locks itself to the front contact of relay C and in attracting its outer armature provides a circuit to hold relay B operated while the armature of relay D is vibrating as the dial restores. Dial 105, in returning tojnormal, interrupts at its impulse contact 106 the circuit of the impulse relay A Upon eachretraction of the armature of relay A the following circuit is closed for the Vertical magnet 210 of the incoming selec tor: grounded armature 211,and back contact of relay 1)", conductor 212, armature and back contactof relay A lower arn'iature and front contact of relay B slow relay C vertical magnet 210, and free pole of battery. On the first step of the selector, off normal springs 213 close the following circuit for relay 214: free pole of battery, relay 214, conductor 215, off normal springs 218, conductors 216, 217, armature andfront contact of relay C to ground at the upper armature and front contact of relay B Relay 21st in attracting its up per armature locks itself over the fol lowing circuit: free pole of battery, relay,

21 i, conductor 215, off normal contact 213,

' GORClUCliOl' 216, armature and back contact ofrotary magnet 218, conductor 21!), upper armature and front contactof relay 21%, to I The lamp will also ductor 227, conductor 228, relay D the end of its stroke, the rotar i ma net 218 I .l a

ovens the lockin circuit traced for relay 21 1. Relay 2-14: in retracting its lower armature opens the circuit of the rotary magnet. If the first trunk is busy, ground is present on the test multiple 2253 thereof, whereby the following circuit is closed to again energize relay 21st: grounded multiple 228, test brush 22%, conductor 225, armature 226 and back contact of relay D, conductors 227, 219, back contact and armature of magnet 218, switch 213, conductor 215, rela 21st tofree pole of battery. Relay 214 in attracting its upper armature again locks itself through the back contact of the rotary n'iagnet and in attracting its lower armature again closes the circuit of the ro tary magnet whereupon the selector brushes are stepped to the next trunk. This interaction of the relay 21st and the rotary magnet is continued until an idle trunk is found which is indicated by the absence of ground on the test multiple 223 thereof. lVhen the rotar magnet, at the end of its stroke, positions the brushes on this idle trunk, no

ground being present, relay 214: does not energize but switching relay D energizes over the following circuit: free pole of battery, relay 214, conductor 215, switch 218, conductor 216, armature and back contact of rotary magnet 218, conductor 210, conconductor 229, lower normal contact of switch 207, conductor 230, to ground at'the upper armature and front contact of relay B R-elay21t is marginal and does not operate in this circuit. Relay D in attracting its armatures 204 and 201 extends the talking conductors through to the selector brushes and cuts off impulse relay A Assuming now that the selector has failed to tindan idle trunk, on the eleventh rotary step, 'SWltCll 207 is operated by the shaft of the selector and, at its upper contacts opens the circuit of the impulse relay A which causes the selector (F to restore. The openingof the loop circuit also causes relay D (Fig. 1) to be permanently .deene'rgized. Whenthe dial 105 reaches its normal position after'bcing rotated for the first digit the contact 108 opens one of the circuits traced wlucu circuits have been holding relay B energized and relay D being inert the other circuit for. relay B is also open. Relay B thereupon releases, the retraction of its inner armature closing the circuit of lamp 107. This circuit includes the front contact of relay 0. The toll operator knows by the illumination of this lamp that the incoming selector has failed tolind an idle trunk. If she fails to notice the lighted lamp and operates the dial for the rest of the digits, this has no effect on the switches because the impulse circuit is openat the right armatures of both. relays B and A, the latter relay being locked'in a circuit including the front contact of relay C. If it were not for this arrangement the impulses of the second digit would operate the incoming selector and the rest of the digits would operate succeeding switches which would either result in. a false connection or useless operation of the switches.

Upon noticing the lighted lamp, the oper ator removes the plug; from the jack, releasing the relays F, C, H, and A. Relay G is unlocked when relay {l operates. in series with relay A of the incoming selector when the elf-normal switch 207 is closed as such selector reaches its normal position.

Assuming, however, that an idle trunk was found, the seizure of the toll transmission selector repeater Fig. 3, in which su -h trunk terminates, causes the closure of the following circuit for impulse relay A thereat, free pole of battery, left hand winding of relay A conductor 300, contact 301, of relay B conductor 302, contact 303 of relay F conductor 309, lower left hand winding of repeating coil 304, conductor 303, multiple terminal 234, brush 233, conductor 232, armature 201 and front contact of relay 1)", conductors 202, 109, inner right armature and alternate contact of'relay G, conductors 110, 111, middle left armature and alternate contact of relay F, relays E and D, impulse spring 106, conductor 112,

out-er left armature and alternate contact of relay F, conductors 113, 114, outer right armature and alternate contact of relay G, conductors 115, 203, armature 204 and alternate contact of relay D conductor 252, brush 250, multiple 251, conductor 307, upper left windingof the repeating coil, conductor 305, contact 306 of relay F conductor 310, contact 311 of relay l3, conductor 312, left winding of relay A" switch 313 operated only on the eleventh rotary step of the sel .ctor, to ground. The impulse relay A in attracting its right armature energizes slow relay 314. This relay in attracting its outer left armature supplies a ground to the test multiples 223 to cause this trunk to test lousy. When the relay 314 operates closes at its right hand armature the following circuit for relay l): ground, right arn'iaturc and front contact of relay 314, conductors 315 and 316, contact 317 of relay G conductor 318, outer right hand armature and back contact of relay F conductor 319, relay D to free pole of battery.

The second operation of the dial by the operator transmits the corresponding digit of the called line causing relay A to transmit impulses over the following circuit to the vertical magnet 320 of the selector repeater: ground, right armature and back contact of relay A inner left armature and front contactof relay 314, conductor 32.1

lar to those of the selector ofFig. 2.

hen the dial returns to normal and maintains the relay A energized, aftera slight interval, slow relay 324 releases. When the relay 324 operated on the first impulse and the selector took its first step, relay 325 corresponding to relay 214 (Fig. 2) operated over the following circuit: free pole of battery, relay 325, upper contact of off normal switch 325, conductor 327 arnIat-ure and front contact of relay 324, conductor'390, armature 329 and back contact of relay 330 to ground. In attracting its inner armature, relay locks itself, this circuit including the armature and back contact of rotary inagi'iet 331. These circuits are simi- Upon the cessation of the impulses and the release of the, slow relay 324, the circuit of the r0- tary magnet is closed as follows: free pole of battery, magnet 331, outer armature and front contact of relay 325, normal contact of relay 324, conductor 390, to ground at the armature 329 of slow relay 330. The rotary magnet advances the brushes onto the terminals of the first trunk and at the end of its stroke opens the locking circuit of the relay which releases opening the circuit of the rotary magnet. If the trunk is busy, relay 325 again energizes over the following circuit: free pole of battery, relay 325, upper contact of switch 326, conductor 32?, armature and back contactof rotary magnet 331, conductor 333, back contact and armature 334 of relay G conductor 335, armature 336 and back contact of relay 330, conductor 337, test brush 338 to ground on the test multiple 339. Relay 325 in attracting' its inner armature again locks up and at its other armature again closes the circuit of the rotary magnet which advances the brushes to the next trunk and at the end 7 of its stroke opens the locking circuit of relay 325 which in retracting its armature opens the circnit of the rotary magnet 331. he switch 3.3 corresponds to the switch 207 of the incoming selectorcircuit, Fig. 2. Its function is to permanently open the circuitof the impulse relayA" on the eleventh rotary stop of the selector, that to safl, if all the trunks in the group are busy. The opening of this circuit releases slow relay 314 which in retracting its outer left a'rma turc releases relay D of the incoming se lector. Relay (D in retracting its armature 211 effects the operation of release magnet 240 whereupon the incoming; selector switch is restored to normal. Relay 314, retracting its inner left-hand arntiatnrs. closes a circuit for release magnet 383 whereupon the selector repeater (Fig. 3) releases. in releasing its immature 201, re-

lay D opens the circuit forrelay D (Fig. 1) whereupon the all trunk busy lamp 107 (Fig. 1) is illuminated as previously described. If, however, an idle trunk found, relay G which corresponds to relay D Fig. 2 operates over the following circuit: free pole of'batter relay 325, upper contact of switch 326, conductor 327, armature and back contact of magnet 331, conductor 333, relayG, conductor 340, upper contact of switch 313, conductors 341, 315,.

to ground at the rightarmature and front contact of relay 314.. Relay is marginal and does not operate in this circuit in series with the relay G Relay G operates and in attracting its armatures 342 and 343 errtends the talking conductors through to the talking brushes 344 and The attraction of the armature 334 of relay G grounds the test brush 33S and consequently test multiples 339 of the selected trunk, causing the same to test busy to other selectors. The contact 340 is made before the contact 3.17 is broken by the armature 347 of the relay G Consequently relay D is main tained energized over the following circuit: free pole of battery, relay. D conductor 319, outer right armature and back contact of relay F conductor 318, contact 346,

armature 347, conductor 348, brush 349,

multiple 350, control conductors 351,400, (Fig. 4), conductor 401, armature 402 and back contact -of relay K, conductor 403, sleeve conductor 450, conductor 352, multiple 339,. brush 333, conductor 337, armature and back contact 336 of relay 330, conductor 335, armature 334 and front contact of relay G conductor 315, to ground at the right armature and front contact ofslow relay 314. Thus, the circuit for relay D (Fig. 3) is maintained closed asthe circuit is extended. The switch of Fig. 4 to which the connection has been extended is a combination toll and local connector containing multiples of ordinary automatic subscribers lines in its bank. Thisswitch is accessible not only to the selector-repeaters of Fig. 3, but also to the local selectors which are used by the subscribers in building up their-own connections. Theseizure of the connector causes the closing of the following circuit for the impulse relayA free poleof battery, upper winding of relay A conductor 404, contact 475 of relay 1), conductor 405, left winding of slow relay J conductor 407,

lowermost armature and back contact of relower right hand winding of the repeating coil 304, resistance 359, conductor 360, inner left armature and front contact of relay D left winding of relay 361, conductors 362, 363, resistance 364, upper right hand winding of repeating coil 304, conductor 365, upper armature and back contact of relay H uppermost armature and front contact of relay G brush 344, multiple 367, tip conductor 410, upper armature and back con tact of relay K conductor 476, back contact 477 of D, lower winding of relay A to ground. hen relay G (Fig. 3) operates a circuit is also closed through the right hand winding of relay 361 which leads over 370, 370, armature 334 and front contact of G, conductor 315, to ground at the armature and front contact of relay 314. The current in the circuit just traced is opposite in direction to that in the left hand winding of this relay. Consequently this relay does not operate at this time. Relays .l' and 21* operate, however, the former at its innermost right armature closing a locking circuit for itself as follows: free pole of battery, right winding and right inner-- most armatureand front contact of J con ductor 431, conductor 415, to ground at the armature 416,.and front contact of slow relay B* which is energized upon the energization of the impulse relay A Relay 1% grounds the sleeve wire 417, leading to the test multiples in the local selectors, this circuit leading from grounded armature 410, conductor 415, to conductor 417.

The returnof the dial to normal in transmitting the tens digit of the wanted number interrupts the circuit of relay A which in vibrating its armatures transmits impulses to the vertical magnet 418 of the'connector. The circuit for the first impulse is as follows: free pole of battery, magnet 418, slow relay 419, right contact of off normal switch 420, conductor 421, lower armature and front Contact of relay B to ground at the armature and back contact of the impulse relay A*. At the first step of the connector, the off normal springs 420 are shifted and the succeeding impulses are transmitted by way of the upper armature and front contact of relay 419 and the contact 42 now closed at the off normal springs 420. Relay F* is operated by its lower winding when relay 419 operates, this circuit including the innermost right armature of relay J" and grounded armature 416 of relay B". Relay F locks up to the sleeve wire 450 in a circuit including armature Y The connector brushes are thus lifted to the desired level and upon the cessation of the impulses, impulse relay A remains energized and relay 419 in series with the vert-ical magnet releases preparing the circuit of the rotary magnet 423. The units impulses pass through the back contact of the impulse relay A", lower armature and front contact of relay B, conductor 421, off normal contact 422, back contact of slow relay 419, con

ductor 42s,. innermost left armature and front contact of relay G conductor 4:25, uppermost armature and back contact of relay H rotary magnet 423 to free pole of battery. The connector is thus stepped around into engagement with the desired line.

If this line is idle, full potential is present on its test multiple 426 through the cut off winding of the line switch, and the following circuit is closed to operate. relay ll: multiple 426, brush 427, conductor 4-28, armature lelO and back contact of relay E. conductor 429, upper winding 6f relay H, conductor 480, right hand armature and back contact of relay G, conductor 1 81, conductor 415, armature 416 of relay B to ground. Relay H in attracting its armature 532 looks itself to the grounded sleeve wire 450 and extends this grounded conductor over conductor 4:33, middle right armature and front contact of relay J conduc- 101'434: to the relay K Relay K in at tracting its armature 402 disconnects the grounded sleeve wire 450 from the, control lead 400 leading back to therelay D, Fig. 3 of the selector repeater. Relay D in retracting its outer left hand armature operates relay F to reverse the current flow in the circuitleading back to the operators cord to energize relay 103 to light the lamp 117 (Fig. 1) as a ringing signal to the toll operator. The circuit for relay F is as follows: free pole of battery, relay F conductor 369, outer left armature and back contact of relay D conductor 370, arma- 1 1 8 33 1 and front contact of relay G conductor 315 to ground at the right armature and front contact of relay 314;. Relay F in attracting its outer right armature applies the following substitute ground to hold up the relay F before it can release in order to prevent ringing from occurring at this time as would occur if this relay released: ground, left hand armature and back of relay 871, conductor 372, outer left armature and back contact of relay B outer right armature and front contact of relay F control conductor 31S, contact 3 16 and armature Set? of relay G conductor 348., brush 34.9, multiple 850, conductor 351, conductor 4-00, front contact and armature 435 and lower winding of relay F to free pole of battery. leasing D and operating F which caused the reversal of direction of the current flow in the loop leading back to the toll operaiors position opens the locking circuit of relay F and unless substitute circuitis provided for holding up relay F as just described, after relay K opcratesthe ringing operation would automatically take place as will appear. This is prevented by applying ground to the control conductor e00 over the circuit traced to hold the The operation of relay K by re-- relay F until the operator, by depressing a key as will be explained, releases relay F to start the automatic ringing operation. The release of the relay D and the consequent energization of relay F as described reverses the direction of current flow in the talkin conductors leading back to the operators position. This reversal operates polarized relay E 1) which releases relays F and C which in deenergizing disconnects the dial from the trunk 110, 114 and connects the trunk through to the calling supervisory relay 103 which now operates in series with the impulse relay A of the connector. Belay 103 in operating lights the calling supervisory lamp 117 as a signal to the toll operator thatthe line desired was found idle by the connector. Relay F also releases relay D. Relay A unlockedfiwhen relay C released. Relays E, C, D, A and B are individual to the dial and common to the trunks at a position. Relays F, J, H and G are individual to a given trunk. The op.- erator now operates ringing key BK which impresses alternating current upon the talking conductors which operates the alternating current relay which in attracting its armature operates the relay 371. This relay in attracting its left armature opens the circuit heretofore traced, which has been holding relay F, Fig. 4, energized. This elay in retracting its armatures 437, 499 connects ringing current to the called line through its upper winding. This ringing current is automatically intermittently applied until the called party removes his re coiver, resulting in an increase in the current through the upper winding of relay l3 causing the same to operate removing the ringing current. The attraction of the armature 4-35 of this relay closes a locking circuit for the same over grounded control conductor 400. The extension of the tip and ring conductors by relayF to the called line operates relay 373 over which talking current is fed to the called line. Relay 373 in operating energizes relay ll which in attracting its outer left hand arma ture applies ground to the conductor 374-, and outer right armature of relay I, conductor 318, contact 34.6, armature 3st? of relay G conductor 3A8, brush 34d), multiple 350, conductors 351, tOO, front contact and armature 435 of relay F lower winding of relay F to battery, to hold up relay F indeprmdcntly of relay 37.1. Belay B in opening its contacts 311, 301 opens the con-' nection of battery through the windings of relay A to the talking conductors 807, 808, leading back to the toll. operators position which causes the deenergization of supervisory relay 103. This relay in retracting its armature extinguisher the supervisory lamp 117 which notifies the operator that the subscriber has responded. Talkingcurrent is fed to the called line over the winding of relay 373 and the repeating coil 304. This talking circuit is a standard repeating coil transmission circuit used in long distance connections. Talking current is fed to the calling line from the distant exchange. During conversation the trunk leading from the left hand windings of repeating coil 304 through the right hand winding of the repeating coil (not shown) at the distantoiiice, is dry, in accordance with standard practice.

Assuming now that the desired line when selected by the connector is busy, the test multiple426, Fig. 4, is grounded. When test wiper 427 is set on the. busy multiple 426, ground is extended over brush 127,0011- ductor 428, armature 440, contact 444 of re lay E conductor 441, armature 442 and back contact of relay H, conductor 443, relay G to free pole of battery. Relay G energizes and when slow relay E* releases, locks itself up over the following circuit: free pole. of battery, relay G, conductor 443, armature 442 and back contact of relay H, conductor 441, make before break contact 498 of relay E right armature and front contact of relay G conductor 431, conductor 415 to ground at the armature 416 and front contact of relay B Relay G in the case of a local call connects busy tone from the source 445 to the calling line. In the case of a toll call this busy tone is not used, a flashing signal being given to the operator instead. Relay Gr in operating due to the line being busy prevents test relay H from operating when slow relay E releases. lVhen busy test relay Gr operates a circuit is closed for relay D from free pole of battery, upper winding of D conductor 47 8, conductor 479, contact 480 of relay K conductor 481, resistance 490, armature 432 and back contact of relay E outer left armature and front contact of G, inner right armature of relay J and front contact, conductor 431, 415 to ground at armature 416 and front contact of B Relay D reverses the direction of current flow through the leftwinding of relay 361 (Fig. 3) which results in this relay operating. The left armature and front contact of relay 361 closes a circuit for operating relay F as follows: battery, relay F, conductor 369, left armature and front contact of relay 361, conductors 376, 370, armature 334 and front contact of G conductor 315 to ground on the right armature andfront contact of relay 314. Relay'F reverses the direction of current flow in the circuit leading back to the operators cord as in the case of an idle line to operate polarized relay E which in turn releases'relay F to connect the talking conductors of the cordthrough to the connector and also releases the common relays 110, D and A as in the case of a free line.

plug from the trunk switching jack.

The right armature of relay 361 connects interrupter 379 to relay 371 which in operating intermittently applies ground to conductor 300 in shunt of the circuit leading over tip conductor 307 back to the operators cord. The circuit of relay 371 leads over the outer right back cont-act of relay 1) to ground at the right armature of relay C The intermittent ground applied to conductor 300 by relay 371 shunts out the relay 103 intermittently which causes the flashing of the lamp 117. The operator thus knows that the desired line is busy and removes the r This causes the release of all switches and the return to normal condition of all the apparatus including the various locked up relays.

During the conversation the called subscriber by moving his hook up and down causes the supervisory lamp 11? at the toll operators position to flash as in the case of manual telephone exchange practice, ithout releasing the switches. This is apparent from the preceding description inasmuch as relay 373 is in circuit with the called line and each time it attracts its armature operates the. relay B which removes battery and ground from the trunk conductors leading back to the supervisor relay 103 and places a bridge across the relay A to hold it operated to prevent release of the switches. lV hen the called subscriber replaces his receiver the lamp 117 lights at the toll operators position, Fig. 1.

The operator may re-ring the subscriber after he has replaced his receiver if she clesires to recall him by actuating her ring ing key RK, which operates relay 0 to op crate 371 which in attracting its left hand armature again releases relay F 4 which initiates the automatic ringing operation at the connector. Thecontrol of this relay F was removed from the relay 371 by the attraction of the outer left armature of relay B when the called subscriber responded and was restored to the relay 371 and consequently tothe operator when the called subscriber replaces the receiver and decnergizes. relay B When the operator desires to break down the connection after the called subscriber has replaced his receiver, she removes the plug from the toll switching jack. This re" leases relay A Fig. 3, which causes the restoration of all the switches. If, however, the operator removes the plug while the called subscriber still has his receiver oil the switch hook, the s *itches are not released since relay A which controls the release is maintainedenergized over the following circuit: battery, left hand winding of relay 1U. conductor 300, armature 380 and front contact of B resistance 381 conductor 312, right hand winding of relay A to ground at the lower normal contact of 1,15.so,e29

switch 313, it being noted that the relay 1% which controls this loop circuit is itself controlled by relay 373 in circuit with the called line and controlled at the switch hook of said line.

The withdrawal of the plug before the called party has restored his receiver connects the battery supplied through relay 102 and the sleeve of the plus from the sleeve multiples of the jacks or this trunk at the ot 161 toll positions but relays J, G and H cooperate to place potential thereon in the following manner: when the plug was inserted in the jack and relay F operated, it closed a circuit. to operate relay G as described. Relay G then looked itself to battery at the right armature of relay J. Relay J is inert at this time since relay H operated when relays F and G operated. Relay ll at its left armature opened the circuit of relay J to prevent the bridge including said relay from interfering with the impulses to the switch. After relay F is released due to relay E operating when the called party answers, relay H is held operated from battery on the sleeves of the plug and jack to hold open the bridge containing relay J. When however, the plug is removed while the calling party still has his receiver off the switchhook relay H releases and relay J being inert due to the trunk 115, 109 being dry, relay G is held locked to battery at the right armature of relay J. Battery is thus supplied over the following path to the sleeves of the jacks right armature and b ack contact of relay J, innermost left armature and front contact of relay G, conductors 118, 119, right armature and back contact of relay H, resistance 120, middle left armature and front contact of relay G, conductor 121, innermost left armature and back contact of relay F, conductor 122 to the sleeve multiples. Relay G is locked in a circuit including the same armature of relay J. When the called party replaces his receiver battery is applied to the trunk 115, 109 as described and relay J operates, unlocking relay G thus removing the busy condition from the jacks of this trunk at all the toll positions at which they appear.

Assuming, however, that the called subscriber has replaced his receiver, when the operator LQHIOVQS the plug, relay A in releasing deenergizes slow relay 814-. Relay 31 1: in retracting its outer left armature removes ground from the sleeve conductor 382 leading to the release relay D whereupon this relay closes the. circuit of release magnet 24-0 as follows: free pole of battery, magnet 2-110, of? normal switch contact 213, lower armaturcs and back contacts of relay B and A to ground at the armature 211 and back contact of relay D Thus the first selector is restored and upon reaching its normal position opens the off normal springs 21.3. The removal of ground from conductor 3-1.5, by the retraction of right hand armature of relay ill'releases relay ti" and the retraction of the right hand armature of relay A and inner left armature of relay 314; closes a circuit for the release magnet at the selector repeater.

'liheslow relay 330 is energized in parallel with the release magnet and opens the cir cult to the test brush 338 during restoration at its armature 336, to prevent interference M6 causes the release of relays A B, J,

Fig. 4, which results in the closure of the following circuit for connector release magnet llO: free pole of battery, magnet 440, lefthand contact of off normal switch 420, back contact and lowermost armature 483 of relay D lower armature and bacl: contactof relay 13 and A to ground. The connector upon reachin normal position restores the off normal switch 420.

' lVhat is claimed is:

1. In a telephone system, the combination at an operators position of trunks terminating thereat, an impulse sender, a signal, means for connecting the impulse sender with any one of said trunks and for actuating said signal, and means for maintaining said signal operated in case a trunk with which the sender is connected is in an unstandard condition.

2. In a telephone system, the combination at an operators position of trunks terminating thereat, cord circuits at said position, an impulse sender, a signal device, meansfor [it its armature 329 it closes connecting said sender with one of-said ready to receive impulses from said sender for effacing said signal, and means for maintaining said signal operated in case said predetermined electric condition is not present on the trunk.

3. In a telephone system, the combination at an operators position of trunks terminating thereat in jacks and at the other end in automatic switches, cord circuits at said position, a signal circuit including a signal device, an impulse sender common to said trunks, means for connecting said sender with one of said trunks responsive to the insertion of a plug of one of said cord circuits in the jack of said trunk, electroma netic means responsive to the insertion of lEZO said plug in said jack for closing said signal circuit, means responsive to current fiow in said trunk tor opening said signal circuit, and means for maintaining said signal circuit closed in case a trunk is in condition to prevent current flowing thereover,

4;. in a telephone system, the combination with a plurality of trunks terminating at an operators position of an impulse sender, means for associating said sender with any one of said trunks responsive to the seizing of said trunk, a signal for each trunk, an operating circuit therefor established in response to the connection of the sender to the corresponding trunk, and means for maintaining said signal circuit established in case a condition exists on the seized trunk that prevents the transmission of impulses thereover.

5. In a telephone system, the combination with a plurality of trunks, switches in which said trunks terminate at an operators position, an impulse sender, means for associating said sender with any one of said established in response to the seizing of the corresponding trunk, and means for maintaining the operating circuit of the seized trunk established responsive to an unstandard condition of said seized trunk.

6. In a telephone system, trunks, a sender common to saidtrunks, a signal for each trunk, means responsive to the seizing of any one of said trunks for connecting the sender therewith and for actuating the corresponding signal, means responsive to a standard condition on said seized trunk for restoring said signal to normal, and means esponsive to an unstandard condition on said seized trunk for maintaining said signal actuated. 1

In witness whereof, I hereunto subscribe my name this 19th day of March A. D, 1924.

RAY L. S'iOKELY. 

